Fuel injector having encased piezo electric actuator

ABSTRACT

An actuator for a fuel injector is disclosed. The actuator has a piezo element, a casing, and at least one end plate. The casing is fabricated through a deep draw process, has bellows, and is configured to house the piezo element. The at least one end plate is hermetically connected to an end portion of the casing.

TECHNICAL FIELD

The present disclosure is directed to a fuel injector and, moreparticularly, to a fuel injector having an encased piezo electricactuator.

BACKGROUND

Common rail fuel systems typically employ multiple closed-nozzle fuelinjectors to inject high pressure fuel into the combustion chambers ofan engine. Each of these fuel injectors include a nozzle assembly havinga cylindrical bore with a nozzle supply passageway and a nozzle outlet.A needle check valve is reciprocatingly disposed within the cylindricalbore and biased toward a closed position where the nozzle outlet isblocked. To inject fuel, the needle check valve is selectively moved toopen the nozzle outlet, thereby allowing high pressure fuel to flow fromthe nozzle supply passageway into the combustion chamber. To move theneedle check valve, a control chamber in fluid communication with a baseof the needle check valve is selectively drained of pressurized fuel tocreate a force imbalance that biases the needle check valve toward theopen position.

A piezo actuator is often used to drain the pressurized fuel from thebase of the needle check valve. Specifically, the piezo actuator, uponbeing energized, expands to move a valve element from a first positionat which pressurized fuel is directed to the base of the needle checkvalve, to a second position at which the pressurized fuel at the base ofthe needle check valve is directed to a drain. Although thisconfiguration is effective for initiating the injection of fuel, it iscritical that the piezo actuator remain isolated and protected from thefuel and other contaminates. In particular, fuel, if allowed to contactthe piezo actuator, can short circuit the actuator or otherwise degradethe performance of the actuator.

One method utilized by injector manufacturers to isolate the actuatorfrom fuel and other contaminates is described in U.S. Pat. No. 6,874,475(the '475 patent) issued to Katsura et al. on Apr. 5, 2005. The '475patent describes a fuel injector for an internal combustion engine. Thefuel injector includes a piezo electric valve actuator enclosed within ahousing. The housing is made of stainless steel cylindrical bellowsconsisting of large-diameter portions and small-diameter portionsarrayed alternately. The bellows allow expansion and contraction of thepiezo electric valve actuator through deformation. The housing ishermetically closed by an upper plate and a lower plate to minimize theingress of fuel. The upper and lower plates are used to transfer forceimparted by the piezo electric valve actuator. One of the lower andupper plates may be formed integral with the housing to improve airtightness.

Although the fuel injector of the '475 patent may sufficiently injectfuel while minimizing piezo/fuel contamination, it may be problematicand costly. For example, because the one of the lower and upper platesand the housing are integral, the material of both the plate and thehousing must be the same. This material, when optimized for thedeformation described above, may not be optimal for force transmission.Similarly, this material, when optimized for the force transmissiondescribed above, may deform poorly. Components fabricated from materialthat is not optimally suited for intended operations may be prone topremature failure. In addition, because a first material used, forexample, to fabricate the housing, may have a higher cost than a secondmaterial best suited for the plate, the integral component functioningas both the housing and the plate, which is made of only the firstmaterial may unnecessarily increase the cost of the fuel injector.Further, the process of fabricating this integral housing/platecomponent may be expensive.

The fuel injector of the present disclosure solves one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

One aspect of the present disclosure is directed to an actuator. Theactuator includes a piezo element, a casing, and at least one end plate.The casing is fabricated through a deep draw process, has bellows, andis configured to house the piezo element. The at least one end plate ishermetically connected to an end portion of the casing.

Another aspect of the present disclosure is directed to a fuel injector.The fuel injector includes a nozzle member, a needle check valve, and anactuator. The nozzle member is configured to receive pressurized fueland has at least one injection orifice. The needle check valve isdisposed with the nozzle member and is movable between a flow blockingposition at which fuel flows through the at least one orifice, and asecond position at which fuel flow through the at least one orifice isblocked. The actuator is operatively connected to move the needle checkvalve between the first and second positions, and includes a piezoelement, a casing, and at least one end plate. The casing is fabricatedthrough a deep draw process, has bellows fabricated through athread-rolling process, and is configured to house the piezo element.The at least one end plate is hermetically connected to an end portionof the casing and is operatively connected to the needle check valve.

Yet another aspect of the present disclosure is directed to a method offabricating a piezo actuator. The method includes forcing a blankagainst a mold to form a cylindrical casing having an open end and aclosed end. The method also includes rotating the cylindrical casing andurging a die having a plurality of equally spaced protrusions into asurface of the cylindrical casing to form bellows in the cylindricalcasing. The method also includes positioning a piezo element within thecylindrical casing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and diagrammatic illustration of an exemplarydisclosed fuel system;

FIG. 2 is a cross-sectional diagrammatic illustration of an exemplarydisclosed fuel injector for the fuel system of FIG. 1; and

FIG. 3 is a cross-sectional illustration of an exemplary disclosedactuator for use with the fuel injector of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates an engine 10 and an exemplary embodiment of a fuelsystem 12. For the purposes of this disclosure, engine 10 is depictedand described as a four-stroke diesel engine. One skilled in the artwill recognize, however, that engine 10 may embody any other type ofinternal combustion engine such as, for example, a gasoline or a gaseousfuel-powered engine. Engine 10 may include an engine block 14 thatdefines a plurality of cylinders 16, a piston 18 slidably disposedwithin each cylinder 16, and a cylinder head 20 associated with eachcylinder 16.

Cylinder 16, piston 18, and cylinder head 20 may form a combustionchamber 22. In the illustrated embodiment, engine 10 includes sixcombustion chambers 22. However, it is contemplated that engine 10 mayinclude a greater or lesser number of combustion chambers 22 and thatcombustion chambers 22 may be disposed in an “in-line” configuration, a“V” configuration, or any other suitable configuration.

As also shown in FIG. 1, engine 10 may include a crankshaft 24 that isrotatably disposed within engine block 14. A connecting rod 26 mayconnect each piston 18 to crankshaft 24 so that a sliding motion ofpiston 18 within each respective cylinder 16 results in a rotation ofcrankshaft 24. Similarly, a rotation of crankshaft 24 may result in asliding motion of piston 18.

Fuel system 12 may include components that cooperate to deliverinjections of pressurized fuel into each combustion chamber 22.Specifically, fuel system 12 may include a tank 28 configured to hold asupply of fuel, and a fuel pumping arrangement 30 configured topressurize the fuel and direct the pressurized fuel to a plurality offuel injectors 32 by way of a common rail 34.

Fuel pumping arrangement 30 may include one or more pumping devices thatfunction to increase the pressure of the fuel and direct one or morepressurized streams of fuel to common rail 34. In one example, fuelpumping arrangement 30 includes a low pressure source 36 and a highpressure source 38 disposed in series and fluidly connected by way of afuel line 40. Low pressure source 36 may be a transfer pump configuredto provide low pressure feed to high pressure source 38. High pressuresource 38 may be configured to receive the low pressure feed and toincrease the pressure of the fuel to the range of about 30-300 MPa. Highpressure source 38 may be connected to common rail 34 by way of a fuelline 42. A check valve 44 may be disposed within fuel line 42 to providefor one-directional flow of fuel from fuel pumping arrangement 30 tocommon rail 34.

One or both of low pressure and high pressure sources 36, 38 may beoperably connected to engine 10 and driven by crankshaft 24. Low and/orhigh pressure sources 36, 38 may be connected with crankshaft 24 in anymanner readily apparent to one skilled in the art where a rotation ofcrankshaft 24 will result in a corresponding rotation of a pump driveshaft. For example, a pump driveshaft 46 of high pressure source 38 isshown in FIG. 1 as being connected to crankshaft 24 through a gear train48. It is contemplated, however, that one or both of low and highpressure sources 36, 38 may alternatively be driven electrically,hydraulically, pneumatically, or in any other appropriate manner.

Fuel injectors 32 may be disposed within cylinder heads 20 and connectedto common rail 34 by way of a plurality of fuel lines 50. Each fuelinjector 32 may be operable to inject an amount of pressurized fuel intoan associated combustion chamber 22 at predetermined timings, fuelpressures, and fuel flow rates. The timing of fuel injection intocombustion chamber 22 may be synchronized with the motion of piston 18.For example, fuel may be injected as piston 18 nears a top-dead-centerposition in a compression stroke to allow forcompression-ignited-combustion of the injected fuel. Alternatively, fuelmay be injected as piston 18 begins the compression stroke headingtowards a top-dead-center position for homogenous charge compressionignition operation. Fuel may also be injected as piston 18 is movingfrom a top-dead-center position towards a bottom-dead-center positionduring an expansion stroke for a late post injection to create areducing atmosphere for aftertreatment regeneration.

As illustrated in FIG. 2, each fuel injector 32 may embody a closednozzle unit fuel injector. Specifically, each fuel injector 32 mayinclude an injector body 52 housing a guide 54, a nozzle member 56, aneedle valve element 58, and an actuator 59.

Injector body 52 may be a cylindrical member configured for assemblywithin cylinder head 20. Injector body 52 may have a central bore 60 forreceiving guide 54 and nozzle member 56, and an opening 62 through whicha tip end 64 of nozzle member 56 may protrude. A sealing member such as,for example, an o-ring (not shown) may be disposed between guide 54 andnozzle member 56 to restrict fuel leakage from fuel injector 32.

Guide 54 may also be a cylindrical member having a central bore 68configured to receive needle valve element 58, and a control chamber 71.Central bore 68 may act as a pressure chamber, holding pressurized fuelthat is continuously supplied from a fuel supply passageway 70. Duringinjection, the pressurized fuel from fuel line 50 may be allowed to flowthrough fuel supply passageway 70 and central bore 68 to nozzle member56.

Control chamber 71 may be selectively drained of or supplied withpressurized fuel to control motion of needle valve element 58.Specifically, a control passageway 73 may fluidly connect a port 75 ofcontrol chamber 71 with actuator 59. Control chamber 71 may also becontinuously supplied with pressurized fluid via a supply passageway 77that is communication with fuel supply passageway 70. A diameter ofsupply passageway 77 may be less than a diameter of control passageway73 to allow for a pressure drop within control chamber 71 when controlpassageway 73 is drained of pressurized fuel.

Nozzle member 56 may likewise embody a cylindrical member having acentral bore 72 that is configured to receive needle valve element 58.Nozzle member 56 may include one or more orifices 80 to allow thepressurized fuel from central bore 68 into combustion chambers 22 ofengine 10.

Needle valve element 58 may be an elongated cylindrical member that isslidingly disposed within housing guide 54 and nozzle member 56. Needlevalve element 58 may be axially movable between a first position atwhich a tip end 82 of needle valve element 58 blocks a flow of fuelthrough orifices 80, and a second position at which orifices 80 are opento allow a flow of fuel into combustion chamber 22.

Needle valve element 58 may be normally biased toward the firstposition. In particular, as seen in FIG. 2, each fuel injector 32 mayinclude a spring 90 disposed between a stop 92 of guide 54 and a seatingsurface 94 of needle valve element 58 to axially bias tip end 82 towardthe orifice-blocking position. A first spacer 96 may be disposed betweenspring 90 and stop 92, and a second spacer 98 may be disposed betweenspring 90 and seating surface 94 to reduce wear of the components withinfuel injector 32.

Needle valve element 58 may have multiple driving hydraulic surfaces. Inparticular, needle valve element 58 may include a hydraulic surface 100tending to drive needle valve element 58 toward the first ororifice-blocking position when acted upon by pressurized fuel, and ahydraulic surface 104 that tends to oppose the bias of spring 90 anddrive needle valve element 58 in the opposite direction toward thesecond or orifice-opening position.

Actuator 59 may be disposed opposite tip end 82 of needle valve element58 to indirectly control the motion of needle valve element 58. Inparticular, actuator 59 may include a three position proportional valveelement 106 disposed within control passageway 73 between controlchamber 71 and tank 28. Proportional valve element 106 may be actuatedto move between a first position at which fuel is allowed to flow fromcontrol chamber 71 to tank 28, a second position at which pressurizedfuel from fuel line 50 flows through control passageway 73 into controlchamber 71, and a third position at which fuel flow through controlpassageway 73 is blocked. The position of proportional valve element 106between the first, second, and third positions may determine a flow rateof the fuel through control passageway 73, as well as the flowdirection. Proportional valve element 106 may be movable between thefirst, second, and third positions in response to an electric currentapplied to a piezo device 108 associated with proportional valve element106. It is contemplated that proportional valve element 106 mayalternatively embody a two-position valve element that is movablebetween only a control chamber draining position and a control chamberfilling position, if desired. It is further contemplated that piezodevice 108 may directly move needle valve element 58, without the use ofproportional valve element 106, if desired.

As illustrated in FIG. 3, piezo device 108 may include a hermeticallysealed assembly of multiple component. In particular, piezo device 108may include a piezo element 110 pre-tensioned by one or more springs112, an outer casing 114, a first end cap 116, a second end cap 118, andelectrical leads 120. Piezo element 110, together with springs 112,first end cap 116, second end cap 118, and electrical leads 120, may besupplied together as a sub-assembly for insertion into and sealingwithin casing 114. It is contemplated that springs 112 may be omittedand the function of pre-tensioning alternatively performed by casing114, first end cap 116, and second end cap 118, if desired.

Piezo element 110 may include one or more columns of piezo electriccrystals. Piezo electric crystals are structures with random domainorientations. These random orientations are asymmetric arrangements ofpositive and negative ions that exhibit permanent dipole behavior. Whenan electric field is applied to the crystals, such as, for example, bythe application of a current, the piezo electric crystals expand alongthe axis of the electric field as the domains line up. Conversely, asthe electric field is removed from the crystals, the piezo electriccrystals retract along the same axis. The piezo electric crystals may bestacked and compressed a predetermined amount by springs 112.

Casing 114 may house piezo element 110 and provide protection againstenvironmental hazards (e.g., fuel contamination, physical damage, etc.).Casing 114 may include a generally cylindrical wall portion 122 and anend portion 124. Wall portion 122 may include a plurality of alternatinglarge and small diameters that together form bellows 126. In oneexample, bellows 126 may extend along casing 114 about the same lengthas piezo element 110, when assembled, to accommodate the expansion andretraction described above. End portion 124 may be integral to wallportion 122, formed of the same material, and bent inward from wallportion 122 toward a central axis (not shown). In one example, endportion 124 may be bent inward through an angle greater than 90 degreesfor engagement with first end cap 116.

Wall and end portions 122, 124 may be formed through a deep drawprocess. Specifically, a metallic blank (not shown) such as, forexample, an aluminum blank, may be forced against a mold (e.g., into afemale mold or over a male mold) to form a substantiallycylindrical-shaped object having an open end and a closed end. In theparticular example depicted in FIG. 3, the aluminum blank was forcedinto a female mold such that end portion 124 was bent through theappropriate angle described above. Once the cylindrical-shaped object isformed, a hole 126 having a diameter less than an inner diameter of wallportion 122 may be made through the closed end of the cylindrical-shapedobject, such that only an annular lip structure remains. Hole 126 may bemade through a shearing process, reaming process, boring process, or anyanother known hole-making process. It is contemplated that wall and endportions 122, 124 may alternatively be formed from a metal blank otherthan aluminum such as, for example, from stainless steel, if desired.

Bellows 126 may be formed within wall portion 122 through athread-rolling process. In particular, the cylindrical-shaped objectdescribed above may be mounted within a machine to rotate or otherwisebe spun about its central axis. During this rotation, one or more dieshaving a plurality of equally spaced, ridge-shaped protrusions may beurged into an outer and/or inner surface of the cylindrical casing,thereby deforming the surface to create bellows within casing 114.

First end cap 116 may be operatively connected to piezo element 110.First end cap 116 may be connected to piezo element 110 to transfer theforce associated with the expansion and contraction of piezo element 110to proportional valve element 106 (referring to FIG. 2). To withstandthe forces generated by the expansion of piezo element 110 and thechemical environment within piezo device 108, first end cap 116 may befabricated from, for example, stainless steel.

To minimize the likelihood of fuel leaking into and contaminating piezodevice 108, first end cap 116 may be hermetically sealed to casing 114.Specifically, first end cap 116 may include an inner face 128, an outerface 130, and a cylindrical surface 132 connecting inner and outer faces128 and 130. Outer face 130 and/or cylindrical surface 132 may bewelded, chemically joined, or otherwise sealed to wall and/or endportions 114, 116, respectively. It is contemplated that multiplesealing locations between casing 114 and first end cap 116 may provideimproved leakage protection for piezo element 110, as compared to asingle sealing location.

Similar to first end cap 116, second end cap 118 may likewise beconnected to piezo element 110 and hermetically sealed to casing 114.Second end cap 118 may be connected to an end of piezo element 110opposing first end cap 116 to transfer the force associated with theexpansion and contraction of piezo element 110 in reverse direction to asupport of fuel injector 32 (referring to FIG. 2). To withstand theforces generated by the expansion of piezo element 110 and the chemicalenvironment within piezo device 108, second end cap 118 may also befabricated from stainless steel. An outer cylindrical surface of secondend cap 118 may be welded, chemically joined, or otherwise sealed towall portion 114.

Electrical leads 120 may embody positive and negative conductors thatextend through second end cap 116 to direct current into and out ofpiezo element 110. Electrical leads 120 may be alternatingly connectedto layers of crystals within piezo element 110 to create a circuitthrough each crystal. Electrical leads 120 may be connected to thecrystals of piezo element 110 in any manner known in the art.

INDUSTRIAL APPLICABILITY

Although illustrated and described above as being utilized inconjunction with a common rail type fuel injector, the disclosed piezodevice may be applicable to any fluid system where it is advantageous toisolate the associated piezo element from the fluid and/or othercontaminates of the system. By isolating the piezo element from thefluid while still allowing movement of the piezo element, the piezodevice may function as intended and have prolonged component life. Inaddition, by producing the isolation solution (e.g., the case housingthe piezo element) from low cost materials through low costmanufacturing methods, the fluid system incorporating the piezo devicemay be economical. The operation of fuel injector 32 will now beexplained.

Needle valve element 58 may be moved by an imbalance of force generatedby fluid pressure. For example, when needle valve element 58 is in thefirst or orifice-blocking position, pressurized fuel from fuel supplypassageway 70 may flow into control chamber 71 to act on hydraulicsurface 100. Simultaneously, pressurized fuel from fuel supplypassageway 70 may flow into central bore 68 in anticipation ofinjection. The force of spring 90 combined with the hydraulic forcecreated at hydraulic surface 100 may be greater than an opposing forcecreated at hydraulic surface 104, thereby causing needle valve element58 to remain in the first position and restrict fuel flow throughorifices 80. To open orifices 80 and inject the pressurized fuel fromcentral bore 68 into combustion chamber 22, proportional valve element106 may be moved to selectively drain the pressurized fuel away fromcontrol chamber 71 and hydraulic surface 100. This decrease in pressureacting on hydraulic surface 100 may allow the opposing force actingacross hydraulic surface 104 to overcome the biasing force of spring 90,thereby moving needle valve element 58 toward the orifice-openingposition. To close orifices 80 and end the injection of pressurizedfuel, proportional valve element 106 may be moved to stop fuel fromdraining away from control chamber 71 and to, instead, fill controlchamber 71 with pressurized fuel.

Proportional valve element 106 may be directly moved by piezo device108. In particular, as current is applied to the crystals of piezoelement 110 via electrical leads 120, the crystals within piezo element110 may expand, resulting in the axial extension of piezo device 108 andthe corresponding connected movement of proportional valve element 106.In contrast, as current is removed from the crystals within piezoelement 110, the crystals may contract, resulting in the axialretraction of piezo device 10 and the corresponding connected movementof proportional valve element 106. It is contemplated that piezo device108 may alternatively move proportional valve element 106 indirectly byway of pilot fluid, if desired.

As the crystals within piezo element 110 expand or contract, casing 114may accommodate the corresponding change in length. In particular, inorder to avoid damage to piezo device 108, as the crystals within piezoelement 110 expand, bellows 126 of casing 114 may deform to increase thelength of casing 114. Conversely, as the crystals within piezo element110 contract, bellows 120 may return casing 114 to its original shape todecrease the length thereof.

The ability of bellows 126 to deform during the expansion andcontraction of piezo element 110 may provide the bias utilized topre-tension piezo element 110, when springs 112 are omitted. In otherwords, after fabrication of casing 114, after first end cap 116 has beenjoined to casing 114, and after piezo element 110 has been inserted intocasing 114, second end cap 118 may be inserted into casing 114 apredetermined distance or inserted with a predetermined force such thatbellows 126 are slightly deformed and the crystals of piezo element 110are pre-tensioned when second end cap 118 is joined to casing 114.Pre-tensioning may be implemented to accommodate manufacturingtolerances and ensure that a majority of the piezo movement istransmitted to proportional valve element 106.

The processes and materials used to fabricate casing 114 may reduce thecost and improve the reliability of piezo device 108 and fuel injector132. Specifically, because deep drawing and thread rolling are bothrelatively low cost manufacturing methods, and because aluminum is arelatively low cost material, the cost of casing 114 may likewise beinexpensive. In addition, because the material used for casing 114 isdissimilar to the material used for first and second end caps 116, 118,each component may be fabricated from the material best suited for itsintended function, without unnecessarily driving up the cost piezodevice 108.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the fuel injector of thepresent disclosure without departing from the scope of the disclosure.Other embodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the fuel injectordisclosed herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope of the invention beingindicated by the following claims and their equivalents.

1. An actuator, comprising: a piezo element; a casing fabricated througha deep draw process, having bellows, and being configured to house thepiezo element; and at least one end plate hermetically connected to anend portion of the casing.
 2. The actuator of claim 1, wherein thebellows are fabricated through a thread-rolling process.
 3. The actuatorof claim 1, wherein the end portion has an inner diameter less than anouter diameter of the at least one end plate.
 4. The actuator of claim3, wherein: the at least one end plate includes an inner face, an outerface, and a cylindrical surface connecting the inner and outer faces;the inner face is operatively connected to the piezo element; and theouter face is hermetically connected to the end portion of the casing.5. The actuator of claim 4, wherein the cylindrical surface is alsohermetically connected to the casing.
 6. The actuator of claim 1,wherein the at least one end plate is a first end plate and the actuatorfurther includes a second end plate hermetically connected to anopposing end of the casing.
 7. The actuator of claim 6, furtherincluding at least one pre-tensioning spring connected to the piezoelement and disposed within the casing between the first and second endplates.
 8. The actuator of claim 6, wherein the first and second endplates, together with the casing, function to pretension the piezoelement.
 9. The actuator of claim 1, wherein the casing is fabricatedfrom a first material and the at least one end plate is fabricated froma second material dissimilar from the first.
 10. The actuator of claim9, wherein the first material is aluminum.
 11. A method of fabricating apiezo actuator, comprising: forcing a blank against a mold to form acylindrical casing having an open end and a closed end; rotating thecylindrical casing; urging a die having a plurality of equally spacedprotrusions into a surface of the cylindrical casing to form bellows inthe cylindrical casing; and positioning a piezo element within thecylindrical casing.
 12. The method of claim 11, further including makinga hole in the closed end of the cylindrical casing.
 13. The method ofclaim 12, wherein the hole has a diameter less than an outer diameter ofthe cylindrical casing.
 14. The method of claim 12, further includinghermetically sealing a periphery of the hole to a first end plate. 15.The method of claim 14, wherein hermetically sealing includeshermetically sealing the periphery of the hole to an outer face of thefirst end plate.
 16. The method of claim 14, further includinghermetically sealing an inner surface of the cylindrical casing to anouter cylindrical surface of the first end plate.
 17. The method ofclaim 14, further including hermetically sealing the open end of thecylindrical casing to a second end plate.
 18. The method of claim 17,wherein hermetically sealing the open end of the cylindrical casing tothe second end plate pretensions the piezo element.
 19. A fuel injector,comprising: a nozzle member configured to receive pressurized fuel andhaving at least one injection orifice; a needle check valve disposedwith the nozzle member and movable between a flow blocking position atwhich fuel flows through the at least one orifice, and a second positionat which fuel flow through the at least one orifice is blocked; and anactuator operatively connected to move the needle check valve betweenthe first and second positions, the actuator including: a piezo element;a casing fabricated through a deep draw process, having bellowsfabricated through a thread-rolling process, and being configured tohouse the piezo element; and at least one end plate hermeticallyconnected to an end portion of the casing and operatively connected tothe needle check valve.
 20. The fuel injector of claim 19, wherein: theend portion has an inner diameter less than an outer diameter of the atleast one end plate; the at least one end plate includes an inner face,an outer face, and a cylindrical surface connecting the inner and outerfaces; the inner face is operatively connected to the piezo element; andthe outer face is hermetically connected to the end portion of thecasing.